This invention relates to an enclosed electrical switchboard and more particularly a shutter mechanism therefor.
Generally, in an enclosed electrical switchboard, a circuit breaker is housed in an enclosed cubicle to be movable therein, and a disconnecting switch is constructed so that it will be separated automatically from the circuit breaker when it moves. Regarding the shutter mechanism which covers the stationery contact of this disconnecting switch, JEM 1153 provides that "in F.sub.2 and G type enclosed switchboard, a shutter should be provided for the opening of an automatically connecting-type disconnecting switch in a main circuit for covering the stationary contact of the disconnecting switch thus securing the safeness of persons who may approach to the opening after the drawn-out of apparatus through the opening. However, the shutter may be eliminated only in a case where substantially no space exists for a person who approaches to the opening of the disconnecting switch and where a live portion is located in the enclosed switchboard at a portion sufficiently remote from a partition wall not touchable by a person unconsciously."
However, the above provision is not applicable in almost all foreign countries and enclosed electrical switchboards for export must include a shutter mechanism. Furthermore, there are many detailed requirements for the shutter mechanism in many foreign countries. Accordingly, to accommodate the various foreign country requirements it has been necessary to provide a shutter mechanism satisfying all such provisions, because design changes in the shutter mechanism for every foreign country is extremely disadvantageous from a manufacturing standpoint as it requires changes in the construction of the circuit breaker and the enclosed switchboard frame mechanism for each country.
Foreign standards (particularly, the U.S. standard: ANSI, the British standard: BS, and, the International standard: IEC) for the shutter mechanism of an enclosed electrical switchboard are summarized as follows:
1. Thickness of plate (ANSI C37.20)
It is requested to use a steel plate having a thickness of more than 2mm and to change the thickness thereof if a plate of other metal is utilized.
2. Operation (ANSI C37.20 IEC 298)
The shutter mechanism should be constructed so that it will be closed automatically at the disconnected position, test position, and drawn-out position of the switchboard.
3. Protection at the shutter closed position (IEC 298)
The degree of protection is classified by the following symbols:
A. IPH 2: to prevent fingers of an operator from approaching the live portion or contacting with an internal movable part. PA1 B. IPH 3: to prevent a wire or a tool having a thickness of more than 2.5mm from approaching the live portion or contacting with an internal movable part. PA1 c. IPH 6: to prevent completely a human body or other equipment from approaching the live portion or contacting with an internal movable part.
4. Locking (IEC 298,BS 162)
A shutter should be provided with means for locking the same at the shutter closed position.
5. Indication of bus bar side (BS 162)
The bus bar side of a shutter should be indicated by a name plate or painting.
6. Manual forced opening (BS 162)
After drawing-out the unit the live portion and no-voltage portion should be openable independently of each other and if the operator's hand is removed, the unit should return automatically to the original position.